The myogenic bHLH protein MyoD can initiate muscle gene expression in most primary cell types and non-transformed cell lines. However, MyoD is unable to initiate such expression in many tumor cell lines. It is thus believed that multiple factors must work with the myogenic factor to turn on gene transcription as mediated by MyoD and one or more of these factors is commonly inactivated during tumor formation in various cell lineages. Two novel domains of MyoD have been characterized that are necessary to initiate transcription of endogenous genes and several proteins capable of interacting with one of these domains (C/H) have been identified using the yeast two hybrid approach. The hypotheses of this proposal are that (1) these two domains of MyoD are necessary to establish the myogenic lineage by facilitating the initiation of gene transcription in native chromatin and (2) these domains recruit factors that work with MyoD as a chromatin remodeling complex. The specific aims of the proposal are to (1) to further characterize the C/H and Box 2 domains in terms of their role in myogenic lineage determination and muscle cell differentiation, (2) functionally characterize factors that interact with these domains, and (3) develop an in vitro chromatin remodeling assay for MyoD and its associated factors.